Method of manufacturing an electrofusion coupler

ABSTRACT

A method is disclosed for the manufacture of an electrofusion coupler, for connecting adjoining lengths of thermoplastics pipes, and which coupler takes the form of a sleeve of thermoplastics material, to receive adjoining ends of adjoining pipes, the sleeve having an electrical resistance heater embedded therein and extended around the sleeve. In the method, a plastics preform is wound with a resistance heating wire, while heating the wire, to melt the surface of the preform, or applying molten plastics to the preform in the vicinity where the wire runs onto the preform, in order to ensure that the heating wire is fully embedded in the preform. A pressing roller may be run over the preform surface before the molten plastics has solidified, in order to smooth over the molten plastics. The preform 10 is subsequently placed in an injection mould and an outer encapsulating jacket is injection moulded around the preform.

FIELD OF THE INVENTION

This invention relates to a method of manufacturing an electrofusioncoupler for use in the construction of thermoplastics pipe systemswherein a welded joint between adjoining ends of adjoining sections ofplastics pipe, or of such a pipe section and a tubular member formingpart of the pipe fitting, valve or the like, is obtained by insertingsuch adjoining ends into such an electrofusion coupler and energisingthe same.

Such an electrofusion coupler may take the form of a sleeve ofthermoplastics material having an electrical resistance heater embeddedtherein and extended around the sleeve. When adjoining pipe ends or thelike are inserted into the sleeve from opposite ends and the resistanceheating wire, and thus the sleeve, is subsequently heated by passing anelectric current through the ire, both the material of the sleeve andthe material of the inserted pipe ends or the like are locally softenedand fused, whereby an intimate connection is obtained, in the form of awelded join which, when the assembly has cooled, is leak tight tofluids. The coupler remains in situ forming a permanent part of thejoint.

Typically, the electrical resistance wire takes the form of coilembedded in the thermoplastics sleeve and coaxial therewith, the wirelying close to the inner surface of the sleeve, the ends of the wirebeing connected to terminal points, exposed on the exterior of thesleeve for connection to a source of electrical current.

DESCRIPTION OF RELATED ART

British Patent No. 2090558 discloses a method of manufacturing anelectrofusion coupler of the above-noted character in which a tubularthermoplastics preform, destined to form the radially inner part of theelectrofusion coupler, is first formed by injection moulding and issubsequently mounted on a rotatable winding mandrel by means of whichthe preform is rotated about its axis to wind on its outer surface ahelical winding of electrical resistance heating wire fed thereto by aguide. The guide incorporates a heater by means of which the wire isheated electrically as it is wound on the preform so that as it is woundon it melts the outer surface of the preform when it touches the sameand thus becomes at least partially embedded in the preform. The wireguide incorporates an electrical heater which heats the wire as itpasses therethrough onto the preform. The preform is provided withterminal pegs at either end, the free end of the wire being attached tothe terminal peg at one end before winding commences and the wire beingattached at its other end to the other terminal peg after winding. Thewound preform is then inserted within a mould in which an outerencapsulating jacket of thermoplastics material is injection mouldedtherearound, becoming united with the preform, the now integral preformand encapsulating jacket forming the finished electrofusion coupler.

SUMMARY OF THE INVENTION

It is among the objects of the present invention to provide animprovement over the method of Patent No. 2090558 which providesimproved and more reliable location of successive turns of the windingon the preform prior to the moulding of the outer, encapsulating jacket.

The term "electrofusion coupler" as used herein is intended to extend,not only to simple tubular couplers intended to connect two pipesections end to end, in axial alignment, but also to any other fittingwhich serves to connect two or more pipes together, such as elbows, teeconnections, tapping saddles, branch connections, etc.

Accordingly it is an object of the invention to provide an improvedelectrofusion coupler of any type falling within the above definition.

According to one aspect of the invention, there is provided a method offorming an electrofusion coupler, as herein defined, comprising forminga preform of thermoplastics material, applying thereto an electricalresistance heating wire and ensuring that the heating wire is fullyembedded in the preform before placing the preform in an injection mouldand moulding, over the preform, in thermoplastics material, an outerencapsulating jacket.

According to another aspect of the invention there is provided a methodof forming an electrofusion coupler comprising forming a tubular preformof thermoplastics material, winding thereon an electrical resistanceheating wire and ensuring that the heating wire is fully embedded in thepreform before placing the wound preform in an injection mould andmoulding, around the preform, in thermoplastics material, an outerencapsulating jacket.

According to a yet further aspect of the invention, there is provided amethod of forming an electrofusion coupler, as herein defined,comprising applying a heating wire to the surface of a support memberand simultaneously or subsequently applying molten thermoplasticsmaterial to the support member to cover the applied wire, whereby thethermoplastics material will solidify on the support member, andsubsequently stripping off from the support member a product formed bysaid thermoplastics material and having said heating wire embeddedtherein.

According to a still further aspect of the invention, there is provideda method of forming an electrofusion coupler comprising winding aheating wire around a mandrel and simultaneously or subsequentlyapplying molten thermoplastics material to the mandrel to cover thewound-on wire, whereby the thermoplastics material will solidify on themandrel, subsequently stripping off from the mandrel a tubular sleeveformed by said thermoplastics material and having said heating wireembedded therein, and subsequently moulding, around said sleeve, anencapsulating jacket of thermoplastics material.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described below by way of example withreference to the accompanying drawings in which:

FIG. 1 is a schematic perspective view showing a known technique forwinding a heating wire around a preform destined to form an inner partof an electrofusion coupler,

FIGS. 2A and 2B are schematic side elevation and plan views respectivelyillustrating a method embodying the invention for winding a heating wirearound a preform,

FIGS. 3A and 3B are views corresponding to FIGS. 2A and 2B butillustrating another method embodying the invention,

FIGS. 4A and 4B are views, corresponding to FIGS. 2A and 2B butillustrating yet another method embodying the invention, and

FIG. 5 is a fragmentary sectional view showing part of an electrofusioncoupler manufactured by a method embodying the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, there is illustrated schematically the winding of atubular thermoplastics preform 10 with electrical resistance heatingwire 12 in the method disclosed in British Patent No. 2090558. Thepreform 10 is mounted on a mandrel (not shown) for rotation about theaxis of the preform, coupled with axial advancement of the preformwhereby the wire 12, led to the rotating preform from a source (such asa storage reel -not shown) is wound around the preform 10 in asubstantially helical winding. The wire 12 is heated before it reachesthe preform by passing through a passage formed through a combinedheating unit and guide 14 and a degree of tension is maintained in thewire as it is wound on so that the wire 12, as it is wound onto thepreform, melts or softens the surface of the latter slightly whereby thewire, as it is wound on, becomes partially embedded in the surface ofthe preform, with a view to locating successive turns of the winding inposition during the subsequent injection moulding of the outerencapsulating jacket. It will be noted that the preform 10 carries, atopposite ends, respective terminal pegs 11, the free end of the wire 12being secured around one terminal peg 11 before winding commences, andthe other end of the wire winding being secured around the otherterminal peg 11 after winding has been completed.

FIGS. 2A and 2B illustrate a variant, embodying the present invention,of the method of FIG. 1. In this variant, the wire 12, heated by theheater 14, is wound around the rotating preform 10 as before, but aforming tool, for example as illustrated, in the form of a roller 16, ispressed against the surface of the preform in the region of the mostrecently applied portion of the wire being wound on. In the exampleshown, the roller 16 is mounted for rotation in a carrier 16a which isin turn displaceable, radially with respect to the mandrel, in a guidewhich is stationary with respect to the heater 14. The carrier is urgedtowards the preform, to press the roller 16 against the preform, by thepressure of a biasing spring. The extent to which the wire is heated,the rotational rate of the preform 10 and the location of the roller 16relative to the point at which the wire being wound on meets the preformare such that the plastics material of the preform in the immediatevicinity of the wound-on wire 12 is still molten or plasticised in theregion upon which the roller 16 bears, with the result that the roller16 forces the molten plastics material over the wound-on wire 12,thereby covering the latter entirely and reliably preventing subsequentdisplacement of the heated wire out of position. The wound -on wire 12is then fully embedded in the preform, as illustrated in FIG. 5.

It will be appreciated that the spreading tool need not take the form ofa roller but may, for example, take the form of a stationary shoe or thelike. In either case, the spreading or forming tool is preferably coatedwith a non-stick material such as PTFE. The forming tool (e.g. roller16) can be used cool or can be heated to assist in spreading thethermoplastics material. The means by which the forming tool (e.g.roller 16) is biased against the surface of the preform can take variousforms, for example a biasing spring, a pneumatic or hydraulic biasingcylinder, gravitational force, etc.

In the technique illustrated in FIGS. 3A and 3B, in which like partshave like reference numerals, as compared with FIGS. 2A and 2B, a thinlayer of thermoplastics material is applied on top of the wire 12 woundonto the preform 10 by a welding technique which utilises an extrusionwelder or which, as shown, utilises a welding gun 18 which directstowards the surface of the rotating preform a jet of hot gas, and afiller rod 19 of thermoplastics material which is fed automatically intothe hot gas jet in the vicinity of the surface of the rotating preformto deposit molten plastics material on top of the wire 12 which has justbeen wound onto the preform. The welding gun 18, (or, in thealternative, the extrusion welder) like the roller 16 in FIGS. 2A and2B, is mounted so as to be fixed with respect to the wire guide 14'which takes the place of or is constituted by, the combined wire guideand heater in the embodiment of FIGS. 2A and 2B. That is to say, it isnot necessary, in the embodiment of FIGS. 3A and 3B, to heat the wire 12before it is wound onto the preform, but it may nevertheless bepreferable to do so.

A spreading or forming tool, such as a roller corresponding to theroller 16 in FIGS. 2A and 2B, may be arranged "downstream" of thewelding gun in the arrangement of FIGS. 3A and 3B, (or of the extrusionwelder, in the alternative), to spread the additional plastics materialapplied evenly over the preform.

FIGS. 4A and 4B illustrate a further variant, in which the welding gunand filler rod of FIGS. 3A and 3B are replaced by a spray-coating device20 which is arranged to apply to the surface of the rotating preform,over a region through which passes the wire 12 just wound on, a spray ofmolten thermoplastics material, which thus covers the wound-on wire 12at the adjacent surface of the preform with a layer of thermoplasticsmaterial as the preform rotates and advances axially during winding onof the wire 12. The device 20 may be of known type in whichthermoplastics material is introduced in powder form into a jet of hotgas directed towards the surface to be spray-coated.

In a variant of the method of FIGS. 4A and 4B, the heating wire is woundaround the preform in the same manner as described with reference toFIG. 1, or even without heating of the wire, and the fully wire woundpreform is subsequently spray coated with thermoplastics material, usinga device such as the device 20, to produce an intermediate preform inwhich the wire 12 is fully embedded in the thermoplastics material, inthe manner illustrated in FIG. 5, before the outer encapsulated jacketis moulded around the preform.

In a further variant, instead of utilising an inner preform which hasbeen formed by injection moulding, an inner sleeve of a thermofusioncoupler may be formed by winding the heating wire 12 onto a suitablyconfigured bare mandrel whilst the latter is rotated and advancedaxially, and simultaneously, in a manner analogous with that describedwith reference to FIGS. 4A and 4B, spray-coating the mandrel andwound-on wire with plastics material as winding proceeds, so that at theend of this step the mandrel is encased in a tubular plastics sleeve inwhich the heating wire is embedded and which sleeve can readily bestripped off the mandrel for subsequent placement within a mould toprovide the outer encapsulation.

In a further variant, the heating wire 12 is wound around the preform insubstantially the manner described with reference to FIG. 1, except thatthe wire is wound cold (i.e. without heating in a heating unit such asunit 14), but under a predetermined tension. When the wire has beenfully wound and secured at its ends to the respective terminal pegs 11,a predetermined heating current is then passed through the wound wire,from end to end, such as to melt the thermoplastics material of thepreform in the immediate vicinity of the wire so that the latter isdrawn by its pre-tensioning, radially inwardly into the thermoplasticsmaterial which "closes" behind the radially inwardly drawn wire, withthe result that the wire becomes totally embedded as illustrated in FIG.5.

It will be appreciated that, in the various embodiments described above,the preform, once the wire has been wound and embedded, is placed in aninjection mould and the outer encapsulating jacket of thermoplasticsmaterial moulded therearound, by injection moulding, substantially asdescribed in British Patent No. 2090558 and with reference to FIG. 1. InFIG. 5, the outer encapsulating jacket is indicated by the reference 13.

As noted above, the methods described with reference to FIGS. 2 to 4Bmay be adapted to electrofusion couplers taking the form of other typesof fitting adapted to connect two or more pipes together, such aselbows, tee connections, tapping saddles, branch connections, etc. Ininstances, for example in the case of saddles, where a part of thefitting intended to be welded to a plastics pipe is not tubular, but,for example, merely arcuate, it may, of course, be necessary to resortto some technique other than straightforward "winding" to apply theheating wire. Thus, for example, the preform, or the wire guide andmeans of applying additional plastics to the applied wire, or thepreform and the wire guide etc., may be arranged to undergo a morecomplex movement so that, for instance, the wire is applied along asinusoidal path.

I claim:
 1. A method of forming an electrofusion coupler, the stepscomprising,applying a heating wire to the outer surface of a tubularpreform along its length in the form of a number of spaced apart loops,covering each loop of the heating wire in thermoplastics material whilesaid heating wire is supported by said support member to completelycover each loop of the wire in said material in a manner to preventsubsequent displacement of the wire relative to the material, andwherein the heating wire is at least partially embedded in said tubularpreform due to the surface of the tubular preform becoming melted in theregion where the heating wire contacts said tubular preform, and moldingaround the material, in thermoplastics material, an outer encapsulatingjacket.
 2. A method according to claim 1, the additional stepsof:rotating said preform during the application of said heating wire tosaid surface and contacting the wound on wire by a pressure means, andcontrolling the extent to which the wire is heated, the rate of rotationof said preform and the point of contact of said pressure means relativeto the point at which the wire being wound meets the plastics materialso that the plastics material in the immediate vicinity of the wound onwire is still molten in the region upon which said pressure meanscontact the material.
 3. A method according to claim 2, comprising theadditional step of heating said pressure means sufficient to assist inthe spreading of the plastics material.
 4. A method according to claim2, comprising the additional step of heating said pressure means.
 5. Amethod of forming an electrofusion coupler comprising the stepsof:forming a tubular preform of thermoplastics material, winding thereonan electrical resistance heating wire, subjecting the wire to a tensionin a heated condition so as to melt the surface of the preform locallyin the region of the wound on wire to effect a partial embedding of thewire in the preform, while the plastics material is still molten,locally subjecting the molten plastics to a spreading action over thepartially embedded wire sufficient to cover the same completely in amanner to prevent subsequent displacement thereof relative to thepreform, and placing the wound preform in an injection mold and molding,around the preform, in thermoplastics material, an outer encapsulatingjacket.
 6. A method according to claim 5, wherein said molten plasticsmaterial is applied by a welding operation.
 7. A method according toclaim 6, wherein said welding operation includes the steps of;deliveringweldable plastics material to said preform, exposing said deliveredplastics material to a hot gas in a manner to cause the material to bedeposited as molten material on top of the wire which has been woundonto the support member.
 8. A method of forming an electrofusion couplercomprising the steps of:forming a tubular preform of thermoplasticsmaterial, winding thereon an electrical resistance heating wire alongits length in the form of a number of spaced apart loops, heating thewire between the time prior to the wire being wound and molten plasticsmaterial is applied to said wire so as to cause the wire to be locallyand partially embedded in the preform, applying molten plastics materialfrom an external source over each loop of the wound-on wire to cover thesame completely in a layer fused integrally with the preform, in amanner to prevent subsequent displacement thereof relative to thepreform, and placing the wound preform in an injection mold and molding,around the preform, in thermoplastics material, an outer encapsulatingjacket.
 9. A method according to claim 8 wherein said molten plasticsmaterial is applied by a spray coating operation, including the stepsof;rotating said preform during said winding of the wire and saidapplying of said plastics material, and applying a spray of moltenmaterial to the surface of the rotating preform over the region throughwhich the wire is immediately wound on the preform sufficient tocompletely cover the wound on wire.
 10. A method according to claim 8,the additional steps of:rotating said preform during said application ofsaid heating wire to said surface, contacting the wound on wire by apressure means, and controlling the extent to which the wire is heated,the rate of rotation of said preform and the point of contact of saidpressure means relative to the point at which the wire being wound meetsthe plastics material so that the plastics material in the immediatevicinity of the wound on wire is still molten in the region upon whichsaid pressure means contact the material.